A new experimental cancer fighting drug has surprised researchers after clinical trials showed that it effectively reduced the size a certain types of breast cancer in women.

The drug was developed by Roche Holding and studies showed that is slowed the spread of the cancer for women with certain types of breast cancer. Results of the study were presented at the American Society of Clinical Oncology's annual meeting.

The study involved the new treatment currently referred to as T-DM1, or trastuzumab emtansine, which combines the cancer drug Herceptin with a chemotherapy medicine which targets the cancer cell directly. The more commonly used chemotherapy treatments target cancer cells but also affects other cells in the body.

"It's a brand-new way of treating HER2-positive breast cancer," lead author Dr. Kimberly Blackwell told CNN. "This will offer a very important therapeutic option for patients faced with HER2-positive metastatic breast cancer."

Researchers involved with the study created the trial to measure progression-free survival, the time treatment starts until the condition gets worse or the patient dies and also the overall survival rate which is measured from the beginning of treatment until the patient dies.

Those involved with this study have been followed for about two years.

Researchers explained that the average progression-free survival for patients receiving T-DM1 was 9.6 months as opposed to 6.4 months for the group receiving alternative treatment. The difference is considered a great improvement.

The study showed that 65 percent of participants who received the T-DM1 treatment were still alive after two years, as opposed to 48 percent of patients who were given an alternate treatment.

"The data are pretty compelling," according Dr. Michael Link, president of the American Society of Clinical Oncology.

"It's sort of a smart bomb kind of therapy, a poison delivered to the tumor … and not a lot of other collateral damage to other organs," he added.